Dear American Mineralogist Readers, Below are the Paper Highlights for this month’s issue of the American Mineralogist: International Journal of Earth and Planetary Materials. You may also view the American Mineralogist Paper Highlights list at https://msaweb.org/MSA/AmMin/ and click the “Editor’s Notes” tab, which will be available shortly after the issue is live. The DOI links below will take you to the abstract on GeoScienceWorld. If you have “IP” access via your institution’s library, it should reveal the whole paper. Consult your institution’s IT department or friendly librarian. If you have an MSA membership, authenticate your login from the American Mineralogist website at http://www.msapubs.org/. On the portal page, click the American Mineralogist link and enter your username (e-mail address) and your password (membership number). Then, search for the paper you want to read via your browser's search tools. (On most PCs, it is control-F, but that may vary for you.) Note that on GSW, you can sign up for a table of contents to be sent to you when the issue is live -- this is a feature open to anyone who registers on the site. Thank you for reading American Mineralogist. Sincerely, Hongwu Xu Paul Tomascak Editors, American Mineralogist American Mineralogist Volume 110; Number 6; 06-01-2025 Atomistic mechanism of Al substitution effects on the ferroelastic post-stishovite transition by high-pressure single-crystal X-ray diffraction Yanyao Zhang, Stella Chariton, Vitali B. Prakapenka, Takuo Okuchi, and Jung-Fu Lin Aluminum and hydrogen can dissolve into stishovite, a common high-pressure form of silica found in subducting oceanic crusts within the mantle transition zone (410–660 km depth) and the upper part of the lower mantle (660–1900 km depth). This dissolution of aluminum can affect the speed of sound and the stishovite to post-stishovite phase transition pressure. This transition can potentially lead to unusual seismic wave velocity behaviors observed in the upper lower mantle. This, in turn, could be linked to the existence of subducting oceanic crusts in the lower mantle. However, the impact of aluminum dissolution on the seismic wave speeds remains unknown. Zhang et al. determined the atomic positions and crystal structures of aluminum-containing stishovite and post-stishovite under high pressure. This study allows a atomistic understanding of how aluminum dissolution influences the elastic properties, and thus, has important implications for our understanding of deep-mantle seismic observations. https://doi.org/10.2138/am-2023-9257 An experimental study of the breakdown of dolomite in H2O at 700 °C, 100 MPa Theodore C. Labotka, David R. Cole, and Michael T. DeAngelis Labotka et al. conducted hydrothermal experiments to determine the mechanism of the reaction dolomite → periclase + calcite + CO2, a reaction observed in contact-metamorphosed dolomite rock. Using single grains and cores of dolomite rock, they reported on the results of experiments with single grains of dolomite, developed a model for the replacement of dolomite by reaction products based on the topochemical, or shrinking-core, process, and applied the model to a simple case of contact metamorphism. The model is broadly applicable to many cases of mineral replacement reactions in hydrothermal systems. https://doi.org/10.2138/am-2024-9368 Cathodoluminescence textures and trace elements in quartz: Constraints on Ag mineralization in adularia-sericite epithermal systems Shen Gao, Xinyu Zou, Albert H. Hofstra, Liangliang Huang, Haijun Yang, Kezhang Qin, Erin E. Marsh, Kaixuan Hui, Jing Xu, Le Wang, Zhenzhen Li, Junxing Zhao, Ri Han, and Guangming Li This study is the first to reveal that epithermal quartz with CL-blue (red-green-blue false color) zonal textures and high-Sb concentrations is related to Ag mineralization that formed by boiling, using SEM-CL images, CL spectra, LA-ICP-MS, electron spin resonance (ESR), fluid inclusion petrography, and geochemical modeling. The results support the previous fluid evolution model in magmatic-hydrothermal systems and help fill the data gap (847 in situ data) of Ag-rich epithermal deposits. The CL textures and trace elements of quartz help understand ore genesis in epithermal systems by identifying veins. https://doi.org/10.2138/am-2024-9415 Formation of giant copper deposits driven by rapid uplift and sudden depressurization Rui Wang, Chenhao Luo, Yingcai Sun, Shaochen Wu, Xiao-Ping Xia, Xiaolin Wang, and Wenjie Xia The post-collisional magmas associated with giant porphyry deposits show low-zircon water contents. The magmas with lower or no mineralization potential have relatively higher water zircon contents. Rapid cooling and depressurization within mid-upper crustal magma chambers drive voluminous volatile exsolution and fluid discharge, causing intense hydrothermal alteration and large-scale mineralization. The uplift rate and depth of granitic bodies are indicators of the potential for mineralization. https://doi.org/10.2138/am-2024-9425 Thermal expansion of römerite under low-temperature conditions Eli Bird, Olivia S. Pardo, Nina Gilkyson, and Jennifer M. Jackson Bird et al. present low-temperature X-ray diffraction data for römerite, a hydrous sulfate with potential relevance to Mars and the icy satellites of Jupiter. These measurements are supported by additional Mössbauer and Raman spectroscopy measurements. The data inform a new model of römerite’s thermal expansion coefficient at temperatures relevant to the planetary bodies in question and constrain additional thermodynamic quantities. These results will aid future studies in physical modeling of planetary surfaces. https://doi.org/10.2138/am-2024-9432 Binding mechanisms of Y and HREE sorption on birnessite: New insights into the formation and sustainable development of regolith-hosted REE deposits Yuzhou Feng, Huayong Chen, Yuanming Pan, Reza Deevsalar, Leo Ka Long Cheung, Ayetullah Tunc, Kenan Cao, Yuxiang Zhu, Renfei Feng, Mohsen Shakouri, Qunfeng Xiao, Ning Chen, Bing Xiao, and Hui Zheng Birnessite is a minor mineral but a major carrier of HREE in regolith-hosted REE deposits. This study shows that birnessite from HREE- and LREE-dominated deposits has different binding mechanisms of Y (and HREE) sorption. These binding mechanisms of Y and HREE sorption on birnessite controlled by ionic strengths not only can account for the REE fractionation responsible for the formation of HREE-dominated deposits from LREE-enriched granites but also have important implications for the sustainable development of regolith-hosted REE deposits. https://doi.org/10.2138/am-2024-9451 Porphyry Cu-Mo mineralization at Anabama Hill, Delamerian Orogen, South Australia: Fertility assessment implied from epidote and chlorite chemistry Wei Hong, Adrian Fabris, Sarah Gilbert, Stacey Curtis, Tom Wise, and Alan S. Collins The Anabama Hill prospect in the Delamerian Orogen of South Australia has features characterized by K-feldspar-rich and epidote-chlorite-dominated alterations intensely superimposed by extensive quartz-white mica-pyrite±chalcopyrite±molybdenite assemblages. Epidote and chlorite sub-grains were analyzed by SEM-MLA and LA-ICP-MS, with additional whole-rock lithochemical analyses, to evaluate the potential of porphyry mineralization. High Sr/Y and V/Sc, and flat to listric-shaped REE fractionation patterns characterize the granodiorite and diorite porphyry, implying amphibole-leading magmatic fractionation due to high water contents in primitive melts. High Fe, Sr, Pb, U, and Bi in epidote and high Mn, Zn, Zr, and U in chlorite provide convincing evidence that the two green minerals are related to magmatic-hydrothermal porphyry fluids rather than regional metamorphism. High Bi, Cu, Sr, Ti, Zr, and U contents in epidote and Ti/Sr and Al/Si ratios of chlorite imply that they are most likely deposit-proximal or near a heat center. Combined with bulk-rock results, proximal-fertility indicators recorded in epidote and chlorite pair indicate potential to produce porphyry Cu mineralization at Anabama Hill. https://doi.org/10.2138/am-2024-9471 Structural rationale for twinning in galena and a possible relation with the lillianite homologous series Massimo Nespolo and Mahamadou Diallo Two reflection twins are known in the literature for galena: on {111} (spinel twin), frequent, and on {114}, rare and lamellar. The galena structure is highly pseudo-symmetric with respect to a reflection about {111}: at the composition plane, the Pb and S coordination change from octahedral to trigonal prismatic, without modification of the bond distances but with a shrinkage of the non-bonding Pb-Pb and S-S distances. The coordination around the composition plane of the {114} twin is instead broken, with too short non-bonding Pb-Pb and S-S distances and empty regions. This study provides insight into the highly different occurrence frequencies of the two twins in galena by studying the structure of the interface between two twinned crystals. https://doi.org/10.2138/am-2024-9484 Mindat.org: The open access mineralogy database to accelerate data-intensive geoscience research Jolyon Ralph, David Von Bargen, Pavel Martynov, Jiyin Zhang, Xiang Que, Anirudh Prabhu, Shaunna M. Morrison, Wenjia Li, Weilin Chen, and Xiaogang Ma Ralph et al. present information about Mindat, one of the largest databases about mineral species and their distributions. The aim is for users to be aware of the characteristics of the records in the database and better plan their usage in research. https://doi.org/10.2138/am-2024-9486 Hanswilkeite, KFeS2, a new peralkaline sulfide mineral Sergey N. Britvin, Mikhail N. Murashko, Maria G. Krzhizhanovskaya, Oleg S. Vereshchagin, Yevgeny Vapnik, Natalia S. Vlasenko, Yulia S. Shelukhina, and Vladimir N. Bocharov Hanswilkeite, KFe3+S2, a new peralkaline sulfide discovered in nature, can be considered as an indicator of an extreme potassium-rich environment superimposed onto anhydrous and oxidizing formation conditions. The latter raises questions regarding its redox compatibility with coexisting oldhamite, CaS. https://doi.org/10.2138/am-2024-9494 Influence of cation disorder on the mineral physics of ankerite Azzurra Zucchini, Tiziana Boffa Ballaran, Maximiliano Fastelli, Davide Comboni, Michael Hanfland, Francesco Frondini, and Paola Comodi The structural evolution and compressibility of ordered and disordered ankerite at pressures up to ~25 GPa were studied using synchrotron single crystal X-ray diffraction in diamond anvil cell. Ordered ankerite (space group R3) undergoes discontinuous phase transition between 12.15 and 13.45 GPa to a high-pressure structure called ankerite-II (space group P1) that has Ca in eight-fold coordination. Disordered ankerite (R3c space group) does not undergo a phase transition in the investigated pressure range. The results provide the basis for further studies of the influence of ankerite on the low-velocity anomalies observed in the mantle wedge. https://doi.org/10.2138/am-2024-9495 Ezochiite and shiranuiite are cuprorhodsite and are not new mineral species Louis J. Cabri and Andrew M. McDonald Cabri and McDonald examined the data for the new mineral species ezochiite and shiranuiite and argued that they are not new unique minerals but rather represent varieties of cuprorhodsite, ideally CuRh2S4. https://doi.org/10.2138/am-2024-9517 Progressive change in dislocation microstructures in shocked calcite with pressure: Characterization of micrometeoroid bombardment on asteroid Ryugu Naotaka Tomioka, Kosuke Kurosawa, Akira Miyake, Yohei Igami, Takayoshi Nagaya, Takaaki Noguchi, Toru Matsumoto, Masaaki Miyahara, and Yusuke Seto The progressive change in the dislocation microstructure of experimentally shocked calcite was studied by transmission electron microscopy. The calcite shows a drastic increase in dislocation density: dislocation nucleation occurs heterogeneously on the slip planes at ~3-6 GPa and homogeneously throughout the crystal above 6 GPa. The microstructural changes are suitable for new efficient pressure barometers for weakly shocked hydrated planetary materials, represented by the regolith particles of the asteroid Ryugu. https://doi.org/10.2138/am-2024-9540